Heparanase cleavage of perlecan heparan sulfate modulates FGF10 activity during ex vivo submandibular gland branching morphogenesis

Abstract

Heparan sulfate proteoglycans are essential for biological processes regulated by fibroblast growth factors (FGFs). Heparan sulfate (HS) regulates the activity of FGFs by acting as a coreceptor at the cell surface, enhancing FGF-FGFR affinity, and being a storage reservoir for FGFs in the extracellular matrix (ECM). Here we demonstrate a critical role for heparanase during mouse submandibular gland (SMG) branching morphogenesis. Heparanase, an endoglycosidase, colocalized with perlecan in the basement membrane and in epithelial clefts of SMGs. Inhibition of heparanase activity in organ culture decreased branching morphogenesis, and this inhibition was rescued specifically by FGF10 and not by other FGFs. By contrast, exogenous heparanase increased SMG branching and MAPK signaling and, surprisingly, when isolated epithelia were cultured in a three-dimensional ECM with FGF10, it increased the number of lateral branches and end buds. In a solid-phase binding assay, an FGF10-FGFR2b complex was released from the ECM by heparanase. In addition, surface plasmon resonance (SPR) analysis showed that FGF10 and the FGF10-FGFR2b complex bound to purified perlecan HS and could be released by heparanase. We used the FGF10-FGFR2b complex as a probe for HS in SMGs, and it colocalized with perlecan in the basement membrane and partly colocalized with syndecan 1 in the epithelium, and binding was reduced by treatment with heparanase. In summary, our results show heparanase releases FGF10 from perlecan HS in the basement membrane, increasing MAPK signaling, epithelial clefting, and lateral branch formation, which results in increased branching morphogenesis.

Heparanase expression and activity influences chondrogenic and osteogenic processes during endochondral bone formation

“…One explanation for the high levels of Ocn seen in the presence of PI-88 may lie with the function of Runx2, the key transcription factor regulating Ocn expression. If inhibition of HPSE disrupts MAPK signaling, known to lie downstream of HPSE [78], then exit from the cell cycle and concomitant up-regulation of Runx2 may be sufficient to increase Ocn expression and support osteogenesis in the presence of PI-88 [79]. The increase in Ocn expression in the growth plate treated with PI-88 is indicative of an advanced stage of chondrocyte hypertrophy or a trans-differentiation of chondrocytes to an osteoblastic like cell, as described [80].…”

Extracellular matrix and cell signalling: the dynamic cooperation of integrin, proteoglycan and growth factor receptor

“…This localisation of growth factors, and thus their signalling, by the ECM probably contributes to the establishment of gradients of the soluble, diffusible growth factor morphogens, which play vital roles in patterning in developmental processes (Kirkpatrick et al 2004, Kreuger et al 2004. Such examples include fibroblast growth factors (FGFs) and vascular endothelial growth factors (VEGFs), both of which bind to HSPG and can be cleaved off from the glycosaminoglycan components of HSPG by the enzyme heparanase and released as soluble ligands (Patel et al 2007), which are discussed in detail later. However, ECM-bound growth factors do not have to be released in soluble form to function.…”

Complexity of Danger: The Diverse Nature of Damage-associated Molecular Patterns

“…The resulting low molecular weight (LMW)-HA fragments accumulate and stimulate TLR2/4 and inflammatory gene expression, thereby promoting angiogenesis and cancer metastasis (7,23,24). Furthermore, active heparan sulfate (HS) fragments generated by heparanase-1 from extracellular barriers (25) and HS proteoglycan sources, such as the basement membrane perlecan (26), the cell surface syndecans (27), and glypicans (28), serve as TLR4-interacting DAMPs (29,30) (Fig. 1).…”